5 research outputs found
The southern churchill, Petrocephalus wesselsi, a new species of mormyrid from South Africa defined by electric organ discharges, genetics, and morphology
East African and south African churchills (Petrocephalus, Mormyridae) were synonymised in 1959 to become
members of a single species of subcontinental, southern African distribution, Petrocephalus catostoma (G¨unther,
1866). By comparison with the type material for P. catostoma from the Ruvuma River and P. stuhlmanni from
the Ruvu River, both of East African origin, we confirm the South African form of churchill to represent a new
species, P. wesselsi, ranging from the northern Limpopo and Incomati systems south to the Pongola River (Natal)
as its southern limit.We also compared churchills from the Sabie River (25 S, South Africa, Incomati system) with
churchills from the Upper Zambezi River (17 S, Namibia), using electric organ discharges (EODs) and morphology.
The duration of an EOD pulse of the South African form (N D 39; 943:2S:E: 18.82 s) is, on average, more than
twice that of the Upper Zambezi form (N D 37; 436:6 15:1 s), and the amplitude of the second head-positive
phase (P2 phase relative to P1 D 1) significantly weaker (0:133 0:0005 vs. 0:472 0:002 for Upper Zambezi
males, 0:363 0:03 for Upper Zambezi females). In contrast to the Upper Zambezi form, the EOD of the South
African form exhibits no difference between the sexes. Fish from the two origins differ significantly in 11 out of 14 anatomical characters studied, confirming molecular genetic differentiation on the species level
Evidence for Parapatric Speciation in the Mormyrid Fish, Pollimyrus castelnaui (Boulenger, 1911), from the Okavango–Upper Zambezi River Systems: P. marianne sp. nov., Defined by Electric Organ Discharges, Morphology and Genetics
We report on parapatric speciation in the mormyrid fish,Pollimyrus castelnaui (Boulenger, 1911), from the Okavango and the Upper Zambezi River systems. We recognise samples from the Zambezi River as a distinct species,
P. marianne, displaying an eastern phenotype of electric organ discharge (EOD) waveform (Type 3) that is distinct
from the western EOD phenotype (Type 1) observed in P. castelnaui samples from the neighbouring Okavango.
Samples from the geographically intermediate Kwando/Linyanti River (a tributary of the Zambezi that is also intermittently connected to the Okavango) presented a more variable third EOD phenotype (Type 2). In 13 out of 14
morphological characters studied, the Zambezi River samples differed significantly from P. castelnaui. Morphologically and in EOD characters, the Kwando/Linyanti fish are distinct from both P. castelnaui and P. marianne.
Sequence analysis of the mitochondrial cytochrome b gene unambiguously reveals that specimens from the Zambezi
River System form a well supported taxon which clearly differs from P. castelnaui from the Okavango (1.5–2.5%
sequence divergence).Within specimens from theKwando–Zambezi System some geographic differentiation can be
detected (nucleotide substitutions up to 0.6%); but groups cannot be resolved with certainty. Significant allozyme
differences were found between the Okavango and all other EOD types from the Upper Zambezi System, and, within the Zambezi System, between the Kwando (Type 2) and Zambezi (Type 3) individuals. The low Wright’s fixation index values, the lack of fixed allele differences, and small genetic distances provide little evidence for speciation between groups within the Zambezi System, but moderate to great fixation index values and significant allele frequency differences were observed between the Okavango and the other fishes. It is concluded that within
the Zambezi System, differentiation between Kwando/Linyanti and Zambezi populations (as revealed by morphology and EOD waveform comparisons) is so recent that substantial genetic (allozyme and mitochondrial sequence)
differences could not have evolved, or were not detected